The goal is to gain an understanding of the morphological basis for inhibitory interactions within the visual cortex. Inhibitory mechanisms play a critical role in shaping the response properties of visual cortical neurons, and the identification of the neural elements involved in this process will provide an important contribution towards understanding the function of visual cortex. We have already successfully used an antiserum to glutamic acid decarboxylase (GAD, the synthetic enzyme for the inhibitory neurotransmitter gamma-aminobutyric acid, GABA) to examine GABAergic neurons in the thalamus, and we now wish to use GAD immunocytochemistry along with other methods to address this issue in the striate cortex. Specifically, we propose to: 1) establish the number, type, and distribution of neurons and terminals which are immunoreactive for GAD and GABA within monkey striate cortex; 2) learn more about the morphology of distinct classes of GABAergic neurons by examining the types of synaptic contacts they receive on their somata, by correlating them with Golgi stained material, and by examining their relation to neuropeptide containing neurons; 3) examine the morphology and the source of prominent GAD and GABA immunoreactive terminals in the geniculate recipient laminae of striate cortex; and 4) establish the contribution made by GABA immunoreactive neurons to interlaminar and intralaminar connections within striate cortex and to projections outside of striate cortex. This research should provide valuable insights into the functional organization of visual cortex and may illustrate fundamental principles that apply to other regions of the cerebral cortex as well.